Carbon nanotubes have a circular cylindrical structure composed of a rolled graphene sheet, and generally have a straw-shaped structure. Carbon nanotubes are classified into single walled carbon nanotubes (SWCNT) composed of a single tube, double walled carbon nanotubes (DWCNT) having a laminated structure (two-layer structure) composed of two tubes having different diameters, and multi-walled carbon nanotubes (MWCNT) having a laminated structure (multi-layer structure) composed of a plurality of tubes having different diameters, and much applied research is being conducted utilizing the properties of these respective structures.
For example, SWCNT may adopt a structure having semiconductor properties depending on the way in which the graphene sheet is rolled, and because they are expected to exhibit superior mobility, applications of these SWCNT to thin-film transistors (TFT) hold considerable promise, and research into such applications is being actively pursued. For example, reports of Non Patent Literatures 1 to 4 and the like indicate that TFTs using carbon nanotubes exhibit performance that is comparable to or exceeds that of silicon.
In those cases where carbon nanotubes are used as a channel semiconductor material, the TFT is produced by either dispersing one or several carbon nanotubes or dispersing a multitude of carbon nanotubes. In the case where a small number of the carbon nanotubes are used, because the length of the carbon nanotubes is generally approximately 1 micro meter or less, microfabrication techniques are required during the production of the TFT, and the so-called channel length between a source electrode and a drain electrode must be produced on the sub-micron scale.
In contrast, in those cases where a multitude of carbon nanotubes are used, because the network of the carbon nanotubes is used as a channel, the length of the channel can be increased, and thus allowing an easy production. As a reported example of a method of producing TFTs by dispersing a multitude of carbon nanotubes, Non-Patent Literature (NPL) 5 and the like are listed.
Furthermore, since DWCNT and MWCNT exhibit high levels of electrical conductivity, applications to electrode materials, wiring materials, antistatic films and transparent electrodes hold considerable expectation, and research into such applications is progressing.
In order to form a thin film by dispersing a multitude of carbon nanotubes, the thin film can be formed easily by using a solvent or dispersion of carbon nanotubes. Non-Patent Literatures 6 to 9 and the like report methods of forming thin films of carbon nanotubes from the solution or dispersion.
By forming a thin film of carbon nanotubes by a process using the solution or dispersion with carbon nanotubes as a material of semiconductor layers, not only by applying hard materials such as glass but also applying resin(s) or plastic(s) to elements, devices or product substrates or materials, flexibility can also be imparted to the overall element, device or product. Moreover, since a coating process can be employed, meaning a production method that employs a coating process or printing process can be used to achieve low costs of the element, device or product.
The present inventor has reported a composition exhibiting excellent dispersibility of carbon nanotubes and storage stability in addition to exhibiting excellent adaptability to a printing device in Patent Literature (PTL) 1. This is a composition containing carbon nanotubes, a solvent and glycol ether(s).
[PTL 1]
    Japanese Patent Publication No. 2010-180263[NPL 1]    S. J Tans et al., Nature, vol. 393, page 49, 1998[NPL 2]    R. Martel et al., Appl. Phys. Lett., 73, 17, page 2447, 1998[NPL 3]    S. Wind et al., Appl. Phys. Lett., 80, 20, page 3817, 2002[NPL 4]    K. Xiao et al., Appl. Phys. Lett., 83, 1, page 150, 2003[NPL 5]    S. Kumar et al., Appl. Phys. Lett., 89, page 143501, 2006[NPL 6]    N. Saran et al., J. Am. Chem. Soc., 126, page 4462, 2004[NPL 7]    Z. Wu et al., Science, vol. 305, page 1273, 2004[NPL 8]    M. Zhang et al., Science, vol. 309, page 1215, 2005[NPL 9]    Y. Zhou et al., Appl. Phys. Lett., 88, page 123109, 2006